The invention described herein was made under, or in the course of, Energy Research and Development Administration Contract No. AT(04-3)-115, Project Agreement Nos. 89 and 94, with Stanford Research Institute.
The present invention relates to nitroaliphatic difluoroformals and processes for the preparation thereof.
Plastic bonded explosives, often referred to as PBX, are widely used in military and civilian applications. Such explosive compositions generally comprise a suitable explosive such as HMX (cyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine), RDX (cyclo-1,3,5-trimethylene-2,4,6-trinitramine), etc., in particle sizes in the range of about 2 to 30 microns dispersed in a suitable explosively energetic fluid phase with a thickener such as colloidal silica or together with a suitable plastic binder, such as an acrylic resin material, and an energetic plasticizer which confers a plastic quality which enables the explosive composition to withstand mechanical shock or thermal changes without fracturing. The plasticizer may also improve molding properties to facilitate fabrication. A suitable plasticizer should have low volatility and a wide temperature range at which the material remains liquid, i.e., a low glass transition temperature, so as to avoid phase changes which might disrupt the explosive, and, desirably, it should contribute to the explosive energy of the PBX composition.
Such plastic explosive compositions are described in detail in U.S. Pat. No. 3,480,490, "Multiphase Extrudable Explosives", issued Nov. 25, 1969, to Milton Finger et al. The plasticizers disclosed therein include liquid explosives of the gem-dinitroaliphatic hydrocarbon class, a particularly useful one being bis(2-fluoro-2,2-dinitroethyl)formal or FEFO. The use of the related compound bis(2-fluoro-2,2-dinitroethyl) difluoroformal or difluoro-FEFO as a plsticizer is disclosed in our application "Fluorodinitroethyl Difluoroformal and Process of Manufacture", Ser. No. 251,878, filed May 10, 1972, now U.S. Pat. No. 3,922,311 issued Nov. 25, 1975.
The synthesis of certain difluoroformals using sulfur tetrafluoride and hydrogen fluoride maintained at temperatures of about 200.degree. to 250.degree. C. for 10 hours has been reported by Aldrich and Sheppard, J. Org. Chem., 29 11 (1964). The synthesis of bis(2-fluoro-2,2-dinitroethyl) difluoroformal using sulfur tetrafluoride and hydrogen fluoride wherein the molar ratio of SF.sub.4 to HF is less than 1 and reaction temperature is maintained in the range of 95.degree. to about 125.degree. C. is described in the above-cited copending application.